Lipids are classified into various categories, among which the most important is fatty acid. Fatty acids are divided into the saturated fatty acid group and the unsaturated fatty acid group according to the presence of a double bond. Animal fats such as butter or beef tallow mainly consist of saturated fatty acids and are characterized by existing in solid state at room temperature. Vegetable fats and fish oil mainly consist of unsaturated fatty acids. Fatty acid has a structure in which carbon atoms are linked as a long chain. In the nomenclature of unsaturated fatty acid, it is designated as delta (Δ) in case of counting the carbon atom at which the double bond appears firstly from the carboxyl terminal and is designated as omega (ω) in case of counting the carbon atom at which the double bond appears firstly from the methyl terminal. In case of omega nomenclature, it is also designated as “n-.” For example, omega-3 fatty acid refers to a fatty acid wherein the first double bond is located on the 3rd carbon-carbon bond from the methyl (CH3—) group. In the same manner, omega-6 fatty acid refers to a fatty acid wherein the first double bond is located on the 6th carbon-carbon bond from the methyl group. In terms of the content of n-3 and n-6 fatty acids in food usually used as a lipid source, most vegetable foods are richer in n-3 and n-6 fatty acids than animal foods. Among edible oils and fats, n-6 fatty acid-enriched examples are corn oil, cottonseed oil, etc.; n-3 fatty acid-enriched examples are linseed oil and fish oils such as salmon oil; and both n-6 fatty acid and n-3 fatty acid-enriched examples in balance are soybean oil and walnut oil. Among n-6 fatty acids and n-3 fatty acids, linoleic acid (LA), α-linolenic acid (LNA) and arachidonic acid (AA) are classified into an essential fatty acid (EFA) group that humans should essentially ingest, and so they are nutritionally important. Specifically, LA and LNA are elongated or desaturated via biosynthesis procedures after digestion to fatty acids having 20 to 22 carbon atoms chain with 4 to 6 carbon-carbon double bonds. Representative examples of such fatty acids are docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Examples of omega-3 fatty acids are alpha linolenic acid, DHA, EPA, etc. Such omega-3 fatty acids are essential in cell generation and regeneration, and are associated with health of the cardiovascular system—e.g., blood pressure, blood coagulation, lowering of cholesterol level, etc. They are also helpful for arthritis, rheumatism, development and regulation of brain and nerve function, health of skin and hair, and optical health. Examples of omega-6 fatty acids are alpha linoleic acid, arachidonic acid, gamma linolenic acid, etc. The functions of omega-6 fatty acids are to prevent arteriosclerosis, heart disease, premenstrual syndrome (PMS), hypercholesterolemia and hypertension, to alleviate pain and inflammation, and to improve the secretion of sex hormones such as estrogen, testosterone, etc. Omega-6 fatty acids are also helpful for hepatic cirrhosis and have efficacy in the prevention of aging, maintenance of skin health, prevention of obesity and diabetes complications, and alleviation of rheumatic arthritis. An example of omega-9 fatty acids is oleic acid.
Some important functions of lipids, when ingested from food or synthesized in the human body, are as follows: First, major constitutional components of cell membranes (phospholipids, glycolipids and steroids); second, storable high-energy source; third, protective membrane and insulating material for subcutaneous tissue or major organs; fourth, facilitation of excitation conduction in myelinated neurons (non-polar lipids); fifth, conversion to various biological active materials (lipid-soluble vitamins, essential fatty acids, steroid hormones, bile acid, prostaglandin, leukotriene, etc.). As can be seen above, lipids play very important and various roles in the human body. Specifically, polyunsaturated fatty acids (PUFA) are not only constitutional components of phospholipids but are converted into prostaglandins (PG), leukotrienes (LT) and important thromboxanes (TX) via in vivo metabolism and then play important roles in maintaining and regulating various physiological phenomena.
Conjugated linoleic acid (CLA) is a kind of fatty acid which is formed by the modification of the chemical structure of linoleic acid. As its name indicates, CLA has conjugated double bonds. CLA has various physiological activities. Up to now, it has been known as having anticancer activity, antioxidant activity, antiarteriosclerotic activity, antibacterial activity as well as prevention and treating effect on various adult diseases. In addition, it has been known that CLA directly acts on adipocytes in the body to prevent them from absorbing fat, and it aids in reduction of body fat—specifically abdominal fat—by reducing adipocytes by increasing apoptosis of adipocytes by means of increasing degradation and metabolic rate of adipocytes, and facilitating the use of fat as energy for strengthening muscle. As a result, CLA has attracted wide attention as a body-slimming material.
As society continues to advance and develop, the desire for a slim figure has been increasing in proportion to improvement of the standard of living. To satisfy such a desire, attempts have been made to develop a body-slimming material, specifically one from natural products. However, many functional materials used in food, beverages, cosmetics and in the pharmaceutical field originate from natural products, and thus most functional materials are unstable to exterior environmental factors such as light, heat, oxygen, etc. and are insoluble in water, conventional organic solvents and oil. As a result, in spite of their remarkable efficacy and/or effect, the use of functional materials is limited. Examples of such materials are too many to enumerate. At present, functional materials are used after being stabilized by methods of emulsification or encapsulation in solution by the use of surfactant or emulsifier. However, such methods cannot sufficiently physically or chemically stabilize functional materials since micelles are coagulated or functional materials are self-degraded by diffusion in solution. Thus, there is a limited practical use in industry. To resolve such problems, many studies are being carried out in each field, but a satisfactory solution has not yet been achieved.